1. Field
Embodiments of the present invention are generally directed to trapping and holding airborne particles, and more particularly, to optical traps which use a focused hollow-beam for trapping and holding both absorbing and non-absorbing airborne particles.
2. Description of Related Art
Airborne particles pose many problems. The ability to trap airborne particles for inspection and/or measurement is important for many applications. Conventional techniques to optically trap airborne particles use either radiative pressure force or photophoretic force. Trapping a particle in air is more difficult than trapping a particle in a liquid (or on a substrate) since the trap must overcome gravity and air turbulence without help from the higher viscosity of a liquid. Thus, very high numerical aperture (NA) optics, typically in excess of 0.9, is required to produce a strong enough gradient force to trap airborne particles. Trapping airborne particles using the photophoretic force may be advantageous in some cases since the photophoretic force can be 4 to 5 orders of magnitude stronger than the gradient force typically used in optical tweezers.
Existing photophoretic force based traps are only capable of trapping absorbing particles while existing laser tweezer systems can only trap non-absorbing particles. However, many potential applications would benefit from the ability to trap airborne particles regardless of their material type.